1. Field
This invention relates to an electrical adapter for an open fixture rated lamp that is unsuitable for a closed fixture rated lamp.
2. Background of Related Art
Metal halide lamps may include a relatively centrally located arc tube situated within the confines of an outer glass bulb. These arc tubes may be made of quartz and operate at high temperatures and high pressures with respect to ordinary incandescent lamps. Under certain conditions (e.g., at the end of the lamp's life) a system failure or internal factors may result in a safety hazard being created, whereby a violent shattering of the arc tube will send hot glass and lamp parts into contact with the bulb glass which, in turn, can break, releasing the hot glass and lamp parts into the surrounding environment. Under such conditions, there is an obvious risk of severe personal injury, fire and/or property damage.
For this reason, normally such conventional metal halide lamps are supported within what may be referred to as “enclosed” fixtures whose structure is designed to contain violently released hot glass and lamps parts. A cover lens may be used in such fixtures. In addition, significant reductions in such potential violent failures can be achieved by relamping before the rated end of the life of the lamp. Another conventional manner in which such potential violent failures is reduced includes the user periodically turning off the lamp to permit lamp cooling, so that upon relighting, a non-violent or less violent lamp failure is facilitated. An open fixture rated lamp is a high pressure metal halide lamp which, at the end of its life, will not explode and emit hazardous shards of glass. Lamps that are open fixture rated may be suitable for operation in open fixture designs. These types of lamps may feature ultraviolet (UV) protective quartz and a secondary shroud surrounding the arc tube to prevent the scatter of glass in the event of a rupture. Open fixture rated metal halide lamps offer significant advantages for users over closed fixture rated lamps, which can shatter at the end of their life. The open fixture rated lamps can broaden luminaire options by (1) eliminating the need for cover lenses, (2) making lamp replacement easier and (3) removing a source of dirt accumulation that reduces light output. Nevertheless, the major reason to select shrouded, open rated lamps is to protect people and property.
In the past, many mogul base metal halide lamps were enclosed rated only. Newer arc chambers now have a smaller size. The small size of the newer arc chambers can make it possible to add a protective, heavy quartz shroud within the lamp body. The heavy shroud provides containment of hot, inner arc particles should a non-passive lamp failure occur. These lamps can be rated for operation in open fixtures. Enclosing a lamp in a fixture for safety reasons can be eliminated. Operating the metal halide lamp in an open fixture also can help eliminate the reduced lighting efficiency and potentially higher operating temperatures brought on by protective fixture enclosures.
An open fixture rated lamp may be visually distinguished from a closed rated fixture lamp. A center contact button design of the lamp's base mates only to an open rated socket used in an open fixture. This ensures continued safe operation of the open fixture by preventing lamping or relamping with a lamp of another type.
The advent of the open fixture rated metal halide lamps has provided an opportunity for users to use those lamps in existing open fixtures. These existing open fixtures may have lamp sockets known as “mogul” threaded sockets. Both the open and closed rated metal halide lamps can have a medium lamp base, which will not thread into the mogul socket.